1. Field of the Invention
The invention relates to a method and an apparatus for the thermal clamping and releasing of tools in shrink chucks.
2. Description of the Prior Art
Shrinkage is a known method for the manufacture of high-speed tools for material-removing workpiece machining. Use is made of so-called shrink chucks, which have a tool reception section with an at least zonally thermally widenable tool reception opening for receiving a tool shank, as well as a clamping section provided in a machine spindle for receiving the clamp chuck and which can e.g. be constructed in the manner of a steep taper or a hollow shank taper. Typical diameters of the tools to be shrunk in, e.g. in the form of drilling, milling or grinding tools can be approximately 3 to 6 mm to approximately 30 to 40 mm. For the manufacture of a tool at least one portion of the tool reception section is heated to such an extent that as a result of thermal expansion the tool reception opening is so widened that the tool shank of a tool to be inserted can be introduced. Following the insertion of the tool shank the portion is cooled in such a way that the tool is held by frictional resistance in the tool reception opening shrunk as a result of cooling. Thus, tools are obtained as if in one piece and the connection between the shrink chuck and inserted tool can be released again at any time by shrinking out in that the tool reception section is heated to such an extent that the inserted tool is removable again from the thermally widened tool reception opening. In the present application generally both the tool part to be inserted, e.g. a milling cutter, and the combination resulting from the assembly of the tool part and the shrink chuck is referred to as a tool.
Shrinkage devices are known in which the heating of the tool reception section is performed during shrinking in and out by means of hot air. By means of a separate cooling device equipped with a fan the cooling time can be reduced to approximately 10 minutes to give a temperature suitable for the manual handling of the shrink chuck. Such devices are inexpensive to provide and are particularly suitable for applications where only small numbers of shrink chucks per time unit have to be handled.
During shrinking in and in particular shrinking out of carbide tools by means of hot air devices, as a result of the different thermal expansion coefficients of the tool material and the shrink chuck material problems do not generally arise, but in the case of tools with HSS and steel shanks, particularly when shrinking out problems can occur, because in this case the thermal expansion behavior of the tool material and the chuck material is similar and with slow heating the tool shank can be enlarged to such an extent in the widening tool reception opening that the tool continues to be held by the widening reception opening and cannot be removed or can only be removed by exerting force.
To avoid these problems it has already been proposed to inductively heat the shrink chucks during thermal clamping and releasing. Energy introduction by means of an induction coil surrounding the shrink chuck can take place so rapidly that a temperature rise of shrunk in tools only occurs to a limited extent by heat conduction. Besides permitting the shrinking out of carbide tools, it reliably permits the shrinking out of tools having essentially the same temperature expansion behavior as the material of the typically steel shrink chuck.
A known, inductive shrinkage device is designed as a table-mounted device and has a box-like casing which can be installed on a table and whose top forms the working surface of the device. Above the working surface is raised a column with vertical guides for a coil holder, to which can be fitted an induction coil above the workstation of the device. An integrated pneumatic cylinder moves the column-guided, air-cooled coil into the working position downwards or back into the upper neutral position. The main clamping range of interest with a 6 to 32 mm tool diameter is covered by three different coils, which can be changeably fitted to the coil holder by means of a snap closure. The working surface of the device formed by the top of the casing is designed as a perforated plate through which an air flow produced by a fan located in the casing can be blown from below through the working surface. Besides the work station located below the coil, the work surface carries several circular cooling stations through which air can be blown from below.
For shrinkage purposes a shrink chuck is engaged in a transportable chuck reception sleeve, which is provided with radial cooling ribs and through which air flows from below on installation in the workstation. Then the previously appropriately selected induction coil for heating the shrink chuck is lowered onto the latter and inductive heating is carried out for shrinking in or out. After inserting or removing the tool the coil is raised again. Then the chuck reception sleeve carrying the still hot shrink chuck is placed on one of the cooling stations. To speed up cooling a separate cooling sleeve with cooling ribs surrounding the tool reception section can be installed. The workstation which has been freed below the induction coil can be used for shrinking the next chuck.
The resulting handling of the device has proved to be problematical. It has also been found that the device is only suitable to a limited extent for a rapid passage of higher numbers, because there is a slow overall system heating. Operators have also considered it to be disadvantageous that in part still hot chucks have to be moved in order to achieve a higher throughput.
The object of the invention is to provide a method and apparatus for the thermal clamping and releasing of tools in shrink chucks, which permit a relaxed, low-fatigue working during shrinking, particularly during the continuous processing of large numbers.
To solve this problem the invention proposes a method for the thermal clamping and release of tools in shrink chucks, a shrink chuck having a tool reception section with an at least zonally thermally widenable tool reception opening for receiving a tool shank and a clamping section for receiving the shrink chuck in a machine spindle, the method comprising a heating of at least part of the tool reception section for widening the tool reception opening and a subsequent active cooling of the tool reception section, the method comprising the following steps:
heating the tool reception section of a first shrink chuck received in a first work station of a shrinking device;
at least one of introducing a tool shank into the tool reception opening of the first shrink chuck and removing a tool from the tool reception opening of the first shrink chuck;
active cooling of the tool reception section of the first shrink chuck received in the first work station;
heating the tool reception section of a second shrink chuck received in a second work station of the shrinking device, the second work station being separate from the first work station of the shrinking device. Further the invention proposes an apparatus for the thermal clamping and release of tools in shrink chucks, a shrink chuck comprising a tool reception section with at least one zonally thermally widenable tool reception opening for receiving a tool shank and a clamping section for receiving the shrink chuck in a machine spindle, the apparatus comprising at least one heating device for heating at least part of the tool reception section and a cooling device for the active cooling of a heated part of the tool reception section, the apparatus comprising
a first work station and
at least one second work station,
wherein a work station is provided for the heating and the active cooling of shrink chucks received in the work station and wherein the work stations and the heating device are movable relative to one another for changing between work stations.
In the case of the thermal clamping or release of tools in shrink chucks according to the invention, there is initially a heating of the tool reception section of a first shrink chuck received in a first work station of a shrinkage device. Then, during the shrinking in of the tool shank of a tool to be shrunk in is introduced into the tool reception opening or during shrinking out a shrunk in tool is removed. In the case of a widened tool reception opening a partial tool change is possible, i.e. the removal of one tool part and directly following the same the introduction of another tool part. There is then an active cooling of the heated tool reception section of the first shrink chuck in the first work station. There is also a heating of the tool reception section of a second shrink tool, which is received in a second work station separate from the first work station.
Thus, there are several, i.e. at least two work stations, at which can be performed both a heating of the tool reception section and also an active cooling thereof and cooling appropriately lasts until the tool reception section has a safe temperature suitable for the manual handling of the shrink chuck, which is e.g. less than 40 or 30 degrees C. The provision of several, e.g. two, three or four work stations makes it possible, compared with known solutions, to achieve significantly improved tool logistics and an improved handling, which is much more agreeable for an operator, because in the case of the sought, high tool throughput it is no longer necessary to remove from a work station a still hot and consequently difficult to manually handle tool.
The method according to the invention also permits a substantially parallel or only slightly deferred working with several shrink chucks, because the heating of the shrink chuck received in the second work station can take place at least partly during the cooling of the first shrink chuck received in the first station, so that high throughput capacities are possible. Several shrinkage cycles (heating, introduction and/or removal of a tool, cooling to handling temperature) can be performed substantially in parallel or only slightly deferred and in time-overlapping manner.
In view of the fact that generally the duration of a shrinkage cycle is determined by the cooling time, in preferred variants a particularly advantageous cooling device for the shrink chucks is provided.
The cooling device is characterized in that it is constructed for cooling the cooling adaptor with a cooling fluid or liquid. Cooling can also be accelerated with the aid of liquid cooling, which can particularly effectively dissipate heat from the tool reception section. Active heat dissipation is particularly advantageous, because generally the duration of a shrinkage cycle is essentially determined by the cooling time. Thus, if the cooling time is reduced, the shrinkage cycles are shortened, so that it is possible to process larger numbers of shrink chucks per time unit. A cooling adaptor through which can flow a cooling liquid can, following the end of heating, be inverted onto the tool reception section with large-area contact or fitted in some other way thereto and rapidly removes heat, e.g. within approximately one minute from the heated tool reception section, so that subsequently it is easily possible to manually handle the said shrink chuck without any burning risk.
For creating a large-area contact it is preferably ensured that the cooling adaptor has a preferably conical reception opening, which is so adapted to the preferably conical outer contour of the tool reception section that there is a good heat conducting press fit between the tool reception section and the cooling adaptor. Corresponding to the shaping of the mainly used shrink chucks, the reception opening has an acute opening angle between approximately 3 and approximately 6xc2x0, being in particular approximately 4.5xc2x0.
Since particularly with acute cone angles, a cooling adaptor mounted in accurately fitting manner may be difficult to remove again from the shrink chuck due to self-retention, in a preferred embodiment the reception opening is widenable for loosening contact between the shrink chuck and cooling adaptor. The reception opening can be e.g. bounded by several springy elements or spring tongues distributed around the circumference of the reception opening.
In order to be able to equally effectively cool all commercially available shrink chucks with the cooling device, preferably with a cooling adaptor, are associated several replaceable change inserts with differently dimensioned reception openings. The change inserts are preferably replaceably fixed without the aid of tools to a coolable part, e.g. a liquid-carrying sleeve. A change insert can be constructed in the manner of a split-clamping sleeve. Thus, an insert with a widenable reception opening can be created, which compared with the coolable cooling adaptor body surrounding it is movable to a limited extent between a contact position and a release position and in the contact position the insert is pressed by the sleeve surrounding it into a real contact with the shrink chuck and in the release position the shrink chuck can easily be released from the cooling adaptor accompanied by the widening of the reception opening. This on the one hand permits a good heat transfer between cooling adaptor and shrink chuck and on the other at all times permits trouble free handling.
Appropriately a cooling adaptor is connected to at least one flexible line, e.g. to a pair of heat-resistant, metal-enveloped hoses, which ensures the supply and removal of cooling liquid and simultaneously makes it possible to substantially freely manually move and therefore easily handle the cooling adaptor.
In a preferred embodiment a particularly effective cooling of shrink chucks is achieved in that the cooling device also has at least one liquid-coolable shrink chuck receptacle with a shrink chuck reception opening for the positionally secured reception of the chuck. This makes it possible to ensure that the clamping section of a received shrink chuck is effectively actively cooled, so that during cooling it can serve as a heat sink in addition to a fitted cooling adaptor. This also ensures that the heat introduced on heating is not spread through the receptacle to the entire shrinkage device, which could lead to a slow heating of the overall system and to operating problems.
Appropriately with a shrink chuck receptacle are associated several replaceable change inserts with differently dimensioned reception openings for adapting the shrink chuck receptacle to shrink chucks with different clamping sections, e.g. hollow shank tapers or steep tapers, so that effective cooling can take place of any conventional shrink chuck.
The cooling device can e.g. be operated with water from domestic mains. For protecting resources it can have a closed coolant circuit. Optionally it is possible to provide a cooling unit connected in as desired so that in particular during permanent operation the cooling liquid is kept at a temperature suitable for effective cooling of typically 15 to 20xc2x0 C.
As illustrated by means of the embodiment, the cooling device can be integrated into a shrinkage device. However, it is also possible to construct the cooling device as a separate entity. Such a preferably transportable cooling device can be used in conjunction with most conventional shrinkage devices, so that on shrinking with the latter the cooling times can be significantly reduced so as to achieve a higher throughput. The features of the cooling device can be useful in all shrinkage devices independently of the nature of the heating device and the number of workstations in a shrinkage device.
Although any type of shrink chuck heating is possible, e.g. hot air, in preferred embodiments inductive heating is provided, which permits a particularly rapid heating of the tool reception section from the outside and consequently particularly facilitates the shrinking out of tools, whose thermal expansion behavior substantially corresponds to that of the shrink chuck. Although several induction coils can be provided, there is preferably only one induction coil for serving all the workstations and for changing between individual workstations the induction coil and workstations can be moved relative to one another. In a preferred embodiment three work stations are arranged in fixed manner on an arc and the induction coil is PivotTable mounted about a vertical pivoting axis in the center of the arc, so that in each case by rotation it can be placed above a work station and for performing the shrinkage process can be lowered vertically onto a shrink chuck in a working position or at the end thereof can be retracted upwards into a normal position.
In certain embodiments the induction device for heating shrink chucks only has one induction coil and is constructed in such a way that with said induction coil it is possible to shrink tools with a wide diameter range from at least 6 to 25 mm. Thus, when changing between different diameter tools, there is no need to replace the coil of the shrinking device. The shrinking device is consequently universally usable and is easy to operate. As no working time has to be wasted for changing coils, apparatuses according to the invention permit higher throughput capacities of shrink chucks to be processed. It is optionally possible to deal with smaller and larger diameters, e.g. up to approximately 32 mm.
As working can take place with a fixed installed induction coil, without any sealing problems it is possible to achieve a particularly effective cooling with cooling liquid of the induction coil, which is particularly advantageous for continuous operation. The induction coil can e.g. be formed by a copper tube or the like through which there is a flow.
For speeding up the individual shrinkage cycles and for ensuring that for each type of shrink chuck (large or small clamping diameter) it is possible to inductively transfer a power or capacity suitable for heating, in preferred embodiments by means of an automatic chuck identification device the type of shrink chuck to be heated is automatically identified and the power of the induction coil is adapted or controlled as a function of said type. For this purpose appropriately the operating voltage applied to the induction coil is progressively increased from the lowest preset voltage until it can be established by means of the current drawn from the generator that an adequate heating power is being provided.
For optimizing inductive heat introduction by means of a preferably mechanical, automatic positioning device there can be an automatic axial positioning of the induction coil on lowering onto the particular shrink chuck. Appropriately by means of an adjustable stop it is ensured that the lowering induction coil stops at a height level in which the electromagnetic alternating field produced by the induction coil is coupled in optimum manner into the section of the tool reception opening or shrink chuck used for tool clamping.
This permits a substantially automated sequence of a shrinkage process, in that by means of a control panel certain of the shrinkage-characterizing parameters are inputted, e.g. the diameter or diameter range and material of the tool to be shrunk in. A microprocessor-controlled cycle can then comprise a motor lowering of the induction coil from a neutral position towards the shrink chuck, a subsequent automatic positioning for fixing the correct axial position relative to the shrink chuck, an automatic identification of the shrink chuck type by means of the power drawn from said chuck, an automatic heating of the shrink chuck performed by means of correspondingly preprogrammed values for the heating time and power and optionally after introducing and/or removing a tool an automatic raising of the induction coil back into the neutral position. During this automatic sequence an operator can prepare the next workstation for a shrinkage process. This advantageous variant of an induction device can also be used with shrinkage devices with only a single workstation or with two or three workstations.
These and further features can be gathered from the claims, description and drawings and the individual features, either singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous constructions.